Magnetic resonance imaging (MRI) is a nuclear magnetic resonance (NMR) technique which may be used clinically to differentiate between normal and abnormal tissues. The .sup.1 H NMR imaging method is based upon differences in water proton concentrations and relaxation rates within different tissue types. The use of contrast agents such as paramagnetic metal chelates to enhance the diagnostic utility of MRI has only recently became practical.
U.S. Pat. No. 4,880,008 to Lauffer discloses in vivo enhancement of NMR relaxivity utilizing chelated paramagnetic ions such as iron(III) and gadolinium(III). The chelating substances include bis, tris, and tetracatechol compounds.
U.S. Pat. No. 5,010,191 to Engelstad et al. discloses imaging agents for in vivo magnetic resonance and scintigraphic imaging, including chelated transition metal and lanthanide metal complexes. The patent discloses a comparison screening protocol including the iron(III) chelate of TIRON.RTM.. However, the patent does not disclose the second sphere iron(III) complex of the salt of disodium-1,2-dihydroxybenzene-3,5-disulfonate having water molecules hydrogen bonded to the ligand groups.